Heat pump outdoor fan control

ABSTRACT

An illustrative example method of controlling a heat pump system includes operating in a defrost mode to provide heat to an outdoor heat exchanger for defrosting at least a portion of the outdoor heat exchanger, controlling a fan to be inoperative during the defrost mode, operating in a heating mode to provide heat within a temperature-conditioned space subsequent to operating in the defrost mode, controlling the fan to remain inoperative for an initial period at a beginning of operating in the heating mode, and controlling the fan to operate during the heating mode after the initial period to cause airflow across at least the portion of the outdoor heat exchanger.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No. 62/791,063, which was filed on Jan. 11, 2019.

BACKGROUND

A variety of systems are available to maintain comfortable temperatures within buildings. Some systems include a refrigerant circuit that operates in a cooling mode to reduce the temperature and humidity within the building or in a heating mode to provide heat within the building. During the heating mode it is possible for frost to accumulate on the heat exchanger fins of the unit located outside the building. Temporarily operating the system in the air-conditioning mode directs heat to the outdoor unit heat exchanger for removing the frost or ice that has accumulated.

SUMMARY

An illustrative example embodiment of a heat pump system includes an indoor heat exchanger configured to be situated inside a temperature-conditioned space, a compressor, an outdoor heat exchanger configured to be situated outside the temperature-conditioned space, and a fan associated with the outdoor heat exchanger. A controller is configured to selectively control the system to operate in a defrost mode to provide heat to the outdoor heat exchanger for defrosting at least a portion of the outdoor heat exchanger, control the fan to be inoperative during the defrost mode, selectively control the system to operate in a heating mode to provide heat within the temperature-conditioned space subsequent to operating in the defrost mode, control the fan to remain inoperative for an initial period at a beginning of the heating mode, and control the fan to operate during the heating mode after the initial period to cause airflow across at least the portion of the outdoor heat exchanger.

In an example embodiment having one or more features of the system of the previous paragraph, the controller is configured to determine when the initial period expires based on one of a temperature of the portion of the outdoor heat exchanger or a temperature of a refrigerant fluid in the outdoor heat exchanger.

In an example embodiment having one or more features of the system of any of the previous paragraphs, the initial period expires when a difference between the temperature of the portion of the outdoor heat exchanger and an outside air temperature satisfies at least one preselected criterion.

In an example embodiment having one or more features of the system of any of the previous paragraphs, the initial period expires when the difference between the temperature of the portion of the outdoor heat exchanger and the outside air temperature is below a threshold.

In an example embodiment having one or more features of the system of any of the previous paragraphs, the threshold is 3° F. (1.7° C.).

In an example embodiment having one or more features of the system of any of the previous paragraphs, the initial period expires when the one of the temperature of the portion of the outdoor heat exchanger or the temperature of the refrigerant fluid in the outdoor heat exchanger falls below an outside air temperature in a vicinity of the outdoor heat exchanger.

In an example embodiment having one or more features of the system of any of the previous paragraphs, the initial period expires when a temperature of the portion of the outdoor heat exchanger is within a preselected range above freezing.

An example embodiment having one or more features of the system of any of the previous paragraphs includes a reversing valve and wherein the controller is configured to control the reversing valve to direct refrigerant fluid from the compressor to the outdoor heat exchanger in the defrost mode and to direct refrigerant fluid from the outdoor heat exchanger to the compressor in the heating mode.

An illustrative example method of controlling a heat pump system includes operating in a defrost mode to provide heat to an outdoor heat exchanger for defrosting at least a portion of the outdoor heat exchanger, controlling an outdoor fan to be inoperative during the defrost mode, operating in a heating mode to provide heat within a temperature-conditioned space subsequent to operating in the defrost mode, controlling the fan to remain inoperative for an initial period at a beginning of operating in the heating mode, and controlling the fan to operate during the heating mode after the initial period to cause airflow across at least the portion of the outdoor heat exchanger.

An example embodiment having one or more features of the method of the previous paragraph includes determining when the initial period expires based on one of a temperature of the portion of the outdoor heat exchanger or a temperature of a refrigerant fluid in the outdoor heat exchanger.

In an example embodiment having one or more features of the method of any of the previous paragraphs, the initial period expires when a difference between the temperature of the portion of the outdoor heat exchanger and an outside air temperature satisfies at least one preselected criterion.

In an example embodiment having one or more features of the method of any of the previous paragraphs, the initial period expires when the difference between the temperature of the portion of the outdoor heat exchanger and the outside air temperature is below a threshold.

In an example embodiment having one or more features of the method of any of the previous paragraphs, the threshold is 3° F. (1.7° C.).

In an example embodiment having one or more features of the method of any of the previous paragraphs, the initial period expires when the one of the temperature of the portion of the outdoor heat exchanger or the temperature of the refrigerant fluid in the outdoor heat exchanger falls below an outside air temperature in a vicinity of the outdoor heat exchanger.

In an example embodiment having one or more features of the method of any of the previous paragraphs, the initial period expires when a temperature of the portion of the outdoor heat exchanger is within a preselected range above freezing.

An example embodiment having one or more features of the method of any of the previous paragraphs includes controlling a reversing valve to direct refrigerant fluid from the compressor to the outdoor heat exchanger in the defrost mode and to direct refrigerant fluid from the outdoor heat exchanger to the compressor in the heating mode.

An example embodiment having one or more features of the method of any of the previous paragraphs includes controlling the initial period to avoid condensation of refrigerant vapor inside the outdoor heat exchanger during the heating mode.

An example embodiment having one or more features of the method of any of the previous paragraphs includes controlling the initial period to direct heat of a refrigerant vapor in the outdoor heat exchanger toward the compressor.

An illustrative example controller includes a processor and memory including instructions that are executable by the processor to perform a method comprising: operating in a defrost mode to provide heat to an outdoor heat exchanger for defrosting at least a portion of the outdoor heat exchanger, controlling a fan associated with the outdoor heat exchanger to be inoperative during the defrost mode, operating in a heating mode to provide heat within a temperature-conditioned space subsequent to operating in the defrost mode, controlling the fan to remain inoperative for an initial period at a beginning of operating in the heating mode, and controlling the fan to operate during the heating mode after the initial period to cause airflow across at least the portion of the outdoor heat exchanger.

In an embodiment having one or more features of the controller of the previous paragraph, the memory includes instructions for determining when the initial period expires based on one of a temperature of the portion of the outdoor heat exchanger or a temperature of a refrigerant fluid in the outdoor heat exchanger. The initial period expires when the temperature of the portion of the outdoor heat exchanger or the temperature of the refrigerant fluid in the outdoor heat exchanger falls below an outside air temperature in a vicinity of the outdoor heat exchanger, or when a temperature of the portion of the outdoor heat exchanger is within a preselected range above freezing.

The various features and advantages of at least one disclosed example embodiment will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates selected portions of a heat pump system.

FIG. 2 is a flow chart diagram summarizing an example control method.

FIG. 3A is a timing diagram showing fan control according to the prior art.

FIG. 3B is a timing diagram showing fan control used in a disclosed example embodiment.

DETAILED DESCRIPTION

Embodiments of this disclosure provide better heat pump performance based on controlling outdoor fan operation when the system transitions from a defrost mode to a heating mode. Controlling the outdoor fan to remain idle at the beginning of the heating mode following the defrost mode allows for stored heat energy to be used for the heating mode and avoids condensation of refrigerant in the outdoor heat exchanger that otherwise would occur.

FIG. 1 schematically illustrates a system 20 that includes a refrigerant circuit capable of operating in several modes. The refrigerant circuit includes an indoor heat exchanger 22, a compressor 24, an outdoor heat exchanger 26 and expansion valves 28 that operate in a known manner The indoor heat exchanger 22 is configured to be situated within a temperature conditioned space 30, such as a building or a residence, and the outdoor heat exchanger 26 is configured to be situated outside the space 30.

The compressor 24 operates in a known manner to pressurize refrigerant fluid within the circuit. A reversing valve 32 controls a direction of fluid flow from the compressor 24 to the rest of the refrigerant circuit. In a cooling mode, the pressurized refrigerant from the compressor 24 flows to the outdoor heat exchanger 26, through one of the expansion valves 28 and to the indoor heat exchanger 22 before returning to the compressor. In a heating mode the reversing valve 32 directs the refrigerant fluid in an opposite direction through the circuit to the indoor heat exchanger 22, through another one of the valves 28 and then the outdoor heat exchanger 26. The way in which the illustrated components operate to provide cooling or heating within the space 30 is known.

During the heating mode when the system 20 operates to provide heating to the space 30, it is possible for frost or ice to build up on the outdoor heat exchanger 26. The illustrated example embodiment includes a controller 34 that determines when such conditions occur, and controls the reversing valve 32 to switch from the heating mode into a defrost mode, which includes directing refrigerant fluid through the circuit in the same direction as used for the cooling mode. In the defrost mode heat from the pressurized refrigerant leaving the compressor 24 enters the outdoor heat exchanger 26 where it melts any frost or ice on the fins of the outdoor heat exchanger 26.

The controller 34, which comprises a processor or other computing device and memory, controls whether the fan 36 operates to direct airflow across the heat exchanger of the outdoor heat exchanger 26. FIG. 2 is a flow chart diagram 40 summarizing an example fan control technique. In some embodiments the memory of the controller 34 contains computer-executable instructions that are executed by the processor to perform a fan control method, such as that illustrated in FIG. 2. At 42, the system is operating in the defrost mode, which may be initiated by the controller 34 using known techniques for determining when defrost is needed or desired. The controller 34 turns off the fan 36 and leaves it inoperative during the defrost mode at 42. After the outdoor heat exchanger 26 is heated sufficiently by the fluid exiting the compressor 24, the controller 34 causes the reversing valve to switch to direct fluid flow in the circuit in the heating mode. At 44, the controller 34 ends the defrost mode and the system returns to heating mode.

The controller 34 controls the fan 36 to remain inoperative at 44 for an initial period of the heating mode following the defrost mode. At 46, the controller 34 determines whether the initial period has expired. If not, the fan 36 remains inoperative at 44. Once the initial period has expired, at 48, the controller 34 activates the fan 36 so that the fan 36 is operative during the heating mode.

The controller 34 determines whether the initial period has expired in some embodiments based on information regarding the temperature of the outdoor heat exchanger 26 or the temperature of refrigerant fluid in the outdoor heat exchanger 26. Known sensors (not illustrated) can provide such information to the controller 34. For example, the initial period lasts as long as the temperature of the outdoor heat exchanger 26 or the refrigerant in the outdoor heat exchanger 26 remains above a threshold temperature. In some embodiments the threshold is preset while in others it varies or is dependent on at least one other parameter that may vary.

In some embodiments, the threshold is preset to be a selected amount above freezing. Using such a threshold contributes to preventing any water remaining on the outside of the outdoor heat exchanger fins from freezing as the initial air flow caused by turning on the fan 36 removes such moisture.

In other embodiments the threshold is based on a current ambient temperature in the vicinity of the outdoor heat exchanger 26. In one such embodiment, the initial period continues until a difference between the temperature of the coil of the outdoor heat exchanger 26 and the outside air temperature satisfies a predetermined criterion. For example, when the difference between the temperature of the heat exchanger coil and the outside air is less than 3 degrees Fahrenheit (1.7 degrees Celsius), the controller 34 turns on the fan 36. Since the outdoor heat exchanger coil will typically be hotter than the outside air at the end of the defrost mode there will be a slight time delay before the coil temperature and the outside air temperature satisfy the criterion for turning on the fan 36.

Waiting until the temperature of the outdoor heat exchanger 26 or the refrigerant within it is below the outside air temperature facilitates absorbing heat from the outside air to contribute to evaporation of the refrigerant instead of losing refrigerant heat by operating the fan while the outdoor heat exchanger temperature exceeds the outside air temperature.

One feature of the defrost mode is that heated fluid from the compressor 24 enters the outdoor heat exchanger 26. Leaving the fan 36 inoperative during the initial period of the heating mode as described above allows for stored heat in the outdoor heat exchanger 26 to be used for providing heat to the temperature conditioned space 30. If the fan 36 turned on immediately at the beginning of the heating mode, that stored heat energy would effectively be lost as the fan 36 draws relatively cooler outside air flow across the heat exchanger coil. Allowing for such stored heat energy recovery improves the efficiency of the heating mode.

Another feature of the fan control of the illustrated example embodiment is that refrigerant condensation in the outdoor heat exchanger 26 is minimized or eliminated. If the fan 36 were turned on at the beginning of the heating mode it is possible or likely that some refrigerant will condense because of the condensation point of the refrigerant and the way in which the outdoor heat exchanger 26 would be cooled by airflow caused by the fan 36. Such condensation can result in excess liquid temporarily trapped in an accumulator, which reduces the amount of refrigerant available and the system capacity. It is also possible for excess liquid in the system to enter the compressor 24, which is undesirable. Leaving the fan 36 inoperative during the initial period avoids such refrigerant condensation.

FIGS. 3A and 3B illustrate a difference between the control implemented in FIG. 2 and the prior art. In FIG. 3A the fan turns on at the same time that the system switches from defrost mode to heating mode as shown at 50. The temperature of the outdoor heat exchanger coil is shown at 52 and the decrease indicated at 54 represents heat loss to the atmosphere and an increased likelihood for condensation.

FIG. 3B, by contrast, includes delaying operation of the fan 36 for the initial period shown at 60. The decrease in the outdoor heat exchanger coil temperature indicated at 62 represents heat recovery and minimized condensation.

The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims. 

I claim:
 1. A heat pump system, comprising: an indoor heat exchanger configured to be situated inside a temperature-conditioned space; a compressor; an outdoor heat exchanger configured to be situated outside the temperature-conditioned space; a fan associated with the outdoor heat exchanger; and a controller that is configured to selectively control the system to operate in a defrost mode to provide heat to the outdoor heat exchanger for defrosting at least a portion of the outdoor heat exchanger, control the fan to be inoperative during the defrost mode, selectively control the system to operate in a heating mode to provide heat within the temperature-conditioned space subsequent to operating in the defrost mode, control the fan to remain inoperative for an initial period at a beginning of the heating mode, and control the fan to operate during the heating mode after the initial period to cause airflow across at least the portion of the outdoor heat exchanger.
 2. The heat pump system of claim 1, wherein the controller is configured to determine when the initial period expires based on one of a temperature of the portion of the outdoor heat exchanger or a temperature of a refrigerant fluid in the outdoor heat exchanger.
 3. The heat pump system of claim 2, wherein the initial period expires when a difference between the temperature of the portion of the outdoor heat exchanger and an outside air temperature satisfies at least one preselected criterion.
 4. The heat pump system of claim 3, wherein the initial period expires when the difference between the temperature of the portion of the outdoor heat exchanger and the outside air temperature is below a threshold.
 5. The heat pump system of claim 4, wherein the threshold is 3° F. (1.7° C.).
 6. The heat pump system of claim 2, wherein the initial period expires when the one of the temperature of the portion of the outdoor heat exchanger or the temperature of the refrigerant fluid in the outdoor heat exchanger falls below an outside air temperature in a vicinity of the outdoor heat exchanger.
 7. The heat pump system of claim 2, wherein the initial period expires when a temperature of the portion of the outdoor heat exchanger is within a preselected range above freezing.
 8. The heat pump system of claim 1, comprising a reversing valve and wherein the controller is configured to control the reversing valve to direct refrigerant fluid from the compressor to the outdoor heat exchanger in the defrost mode and to direct refrigerant fluid from the outdoor heat exchanger to the compressor in the heating mode.
 9. A method of controlling a heat pump system that includes an indoor heat exchanger configured to be situated inside a temperature-conditioned space, a compressor, an outdoor heat exchanger configured to be situated outside the temperature-conditioned space, and a fan associated with the outdoor heat exchanger, the method comprising: operating in a defrost mode to provide heat to the outdoor heat exchanger for defrosting at least a portion of the outdoor heat exchanger, controlling the fan to be inoperative during the defrost mode, operating in a heating mode to provide heat within the temperature-conditioned space subsequent to operating in the defrost mode, controlling the fan to remain inoperative for an initial period at a beginning of operating in the heating mode, and controlling the fan to operate during the heating mode after the initial period to cause airflow across at least the portion of the outdoor heat exchanger.
 10. The method of claim 9, comprising determining when the initial period expires based on one of a temperature of the portion of the outdoor heat exchanger or a temperature of a refrigerant fluid in the outdoor heat exchanger.
 11. The method of claim 10, wherein the initial period expires when a difference between the temperature of the portion of the outdoor heat exchanger and an outside air temperature satisfies at least one preselected criterion.
 12. The method of claim 11, wherein the initial period expires when the difference between the temperature of the portion of the outdoor heat exchanger and the outside air temperature is below a threshold.
 13. The method of claim 12, wherein the threshold is 3° F. (1.7° C.).
 14. The method of claim 10, wherein the initial period expires when the one of the temperature of the portion of the outdoor heat exchanger or the temperature of the refrigerant fluid in the outdoor heat exchanger falls below an outside air temperature in a vicinity of the outdoor heat exchanger.
 15. The method of claim 10, wherein the initial period expires when a temperature of the portion of the outdoor heat exchanger is within a preselected range above freezing.
 16. The method of claim 9, comprising controlling a reversing valve to direct refrigerant fluid from the compressor to the outdoor heat exchanger in the defrost mode and to direct refrigerant fluid from the outdoor heat exchanger to the compressor in the heating mode.
 17. The method of claim 9, comprising controlling the initial period to avoid condensation of refrigerant vapor inside the outdoor heat exchanger during the heating mode.
 18. The method of claim 9, comprising controlling the initial period to direct heat of a refrigerant vapor in the outdoor heat exchanger toward the compressor.
 19. A controller comprising a processor and memory including instructions that are executable by the processor to perform a method comprising: operating in a defrost mode to provide heat to an outdoor heat exchanger for defrosting at least a portion of the outdoor heat exchanger, controlling a fan associated with the outdoor heat exchanger to be inoperative during the defrost mode, operating in a heating mode to provide heat within a temperature-conditioned space subsequent to operating in the defrost mode, controlling the fan to remain inoperative for an initial period at a beginning of operating in the heating mode, and controlling the fan to operate during the heating mode after the initial period to cause airflow across at least the portion of the outdoor heat exchanger.
 20. The controller of claim 19, wherein the memory includes instructions for determining when the initial period expires based on one of a temperature of the portion of the outdoor heat exchanger or a temperature of a refrigerant fluid in the outdoor heat exchanger; and the initial period expires when the one of the temperature of the portion of the outdoor heat exchanger or the temperature of the refrigerant fluid in the outdoor heat exchanger falls below an outside air temperature in a vicinity of the outdoor heat exchanger, or the initial period expires when a temperature of the portion of the outdoor heat exchanger is within a preselected range above freezing. 